This invention relates to a process for treating cereal grains so as to produce a product which is substantially free of embryo, bran and aleurone tissues, and wherein substantially all of the starch granules from the endosperm portion of the grain are maintained in an intact, ungelatinized form and the protein is maintained in a dispersed and substantially undenatured state. While the process of the present invention may be applied to cereal grains such as wheat, rye and triticale, it is principally designed to treat oats (Avena species) which is a nutritious cereal grain and which can be grown extensively in temperature zones, such as Canada, but which heretofore has not been used extensively for human food due to the lack of appropriate technologies. Although certain technologies do exist for the fractionation of the oat kernel into starch, protein, bran and lipid components (U.S. Pat. No. 4,028,468 and Canadian Pat. No. 1,080,700), a satisfactory technology has not been developed which will produce high yields of a refined oat flour. Attempts to roller mill oats, by conventional wheat milling technologies, have for the most part failed because the oat kernel is too soft in texture and too high in lipid content to permit efficient bran and endosperm separation, properties which frequently result in clogging of the rollers. Over many years other ways to use the oat kernel have been sought which have led to the common practice of steaming and rolling of oats to produce an oat flake. These flakes may be ground to a specific particle size to produce a product, which is traded as an article of commerce, referred to as "oat flour". This product is, in fact, not a flour in the usual sense e.g. wheat flour, but is high in crude fiber and ash content being substantially a totally comminuted oat groat. The fact that oats have only been processed into these semi-refined states has greatly limited the number of food products wherein oats can be used as a major ingredient. The lack of suitable technology is surprising considering the fact that oats are the most nutritious of all of the cereal grains, having the least deficient and best balanced protein component.
The technology required to wet-mill oat kernels to yield refined component ingredients (U.S. Pat. No. 4,028,468) has met with some experimental success but is not yet employed commercially. A frequently encountered problem is the development of solution viscosity during aqueous extraction, which is believed attributable to the presence in the seed of polysaccharide gums (.beta.-glucans). These gums are normally associated with cell walls, are at least partially soluble in water, and result in a sticky viscous matrix which makes it very difficult to prepare both bran-free flour or other refined components on a commercial basis.
Canadian Pat. No. 1,080,700 describes a technology wherein oat groats (i.e. oat kernels which have had the outer hulls removed) are milled in the presence of an organic solvent, and fractionated using a plurality of hydrocyclones to yield fractions of varying protein content and a liquid stream from which an oil can be recovered. This is a relatively novel approach and the products have yet to be fully evaluated from the standpoint of end-use or functionality. No details are available pointing to the influence (either positive or negative) of non-polar organic solvents on the basic physiochemical properties of the various product streams.
Canadian Pat. No. 1,028,552 describes a procedure for extracting salt-soluble proteins from oats. In this process, the whole ground oat flour is treated in dispersion with added glucanase enzyme to destroy the gums concommitantly with the extraction of the proteins into the salt solution. While this process is a step in the isolation of one of the protein fractions from oats, it is not a procedure to isolate all major oat seed components.
Canadian Pat. Nos. 956,535 (corresponding to U.S. Pat. No. 3,851,085) and 1,061,267 describe processes for hydroprocessing of wheat although such processes may also be applied to other cereal grains such as rye and oats. In these processes, cereal grain is steeped in an aqueous acid medium having a pH in the range 0.8 to 2.5, at a temperature in the range 18.degree. to 45.degree. C. for sufficient time to absorb medium equivalent to 56-95% by weight of the grain. The steeped grain is then crushed or squeezed, so as to split the grain and expose the endosperm as a soft or pliable mass. The crushed grain is then macerated in an aqueous acid medium so as to disengage the softened endosperm from the outer bran layers, in the form of an endosperm dispersion which can then be spray dried.
Although these processes are effective, considerable energy is required to crush the softened grain and expel sufficient of the endosperm to provide an economically acceptable yield. Furthermore, the use of extremely acid steeping or macerating media is likely to prove detrimental to the starch granules of most grains and to subsequent rheological behaviour of recovered flour.
It is therefore an object of the present invention to provide an improved process for efficient separation of the endosperm from the remaining portions of the grain seed, in particular oats (Avena species), without using conventional dry milling and grinding equipment and without the use of potentially hazardous organic solvents.
Another object is to provide a low fibre, off-white oat flour of endosperm origin, said material, either in the wet or dried state, being a potential starting material for further fractionation processes.